also, agriculture likely predated writing. agriculture is what allowed for surpluses of food and the creation of cities, where writing, religion, and whatever other various aspects of culture would be cultivated.

Spoken language was certainly a great invention and it is pretty impossible to envision human civilization without it. I think one could take issue with the idea that written language is impossible without spoken language though. The earliest writing systems were pictograms (picture representations) and didn't have any relationship to the spoken language (which in most cases were still primitive and undeveloped ). Over time the pictures begin to include representations of the spoken language as well. You can really see it in the Chinese family of languages which hasn't changed all that much in thousands of years, and is made up significantly of pictograms but with some phonetic (spoken) elements placed into it over time. It isn't a wholly pictorial language but it isn't principally based on phonetics either. So basically writing and spoken language (or at least the kind of complex spoken languages that we think of when we use the phrase ) developed along together.

Writing has allowed for countless human advancements, including the agricultural advancements you described, for it allowed for a counting system to help keep track of agricultural goods.